Built on Facts

Archives for August, 2008

GPS Tracking

MarkCC on Good Math, Bad Math has been posting lately on encryption and privacy. As usual, technology has increased the number of ways the government can read your mail, but it has also increased the ways you can hide your communications as well. Modern open-source encryption is very secure and all other things being equal…

Theory and Correlation

In quantum mechanics, particles like electrons can be observed in one of two spin states: up or down. The theory, however, doesn’t require the state to be completely determined before we look at it. Any given electron doesn’t have to be in one of those spin eigenstates; it can be in a superposition of spin…

Crow for Tuesday Breakfast

Sunday night I was thinking about what to write for Monday morning and settled on the moment of inertia of the tires on a vehicle. If I may say so, it’s a pretty good illustration for an interesting topic. Friction was a possible hitch for my proposed experiment, but I figured that cars were specifically…

Under (tire) Pressure

If you live on flat terrain like I do, you might not get a chance to experiment with your car coasting down hills in neutral. It’s kind of dangerous even if you can. But let’s say you’re on the top of your driveway and beginning from a stop you coast down to the street below.…

Sunday Function

I trust you’re having a relaxing Sunday? Mathematical physics can be relaxing too, especially when you just look at it. We’re just going to look at this one. In fact, this is a literal mathematical instantiation of Sunday relaxation. If you fix a wire or a rope at two points and let it hang naturally,…

Magnificent Desolation

This is K2. 11 people died this month trying to climb it. At 28,251 ft (8,611 meters), K2 is the second highest mountain on this planet, and is technically a much more difficult climb than Everest. I’ve never climbed anything higher than a few hundred feet. Even a passenger jet slashing through the darkness will…

The Final Countdown

The Intro Physics II final exam was this week. The signs were all there. 1. It was a summer class. Therefore a fairly high proportion of the students were taking it again after having failed it previously. 2. The class switched professors two weeks before the final. The first professor is a skilled scientist but,…

The Downward Spiral

In 1909, Ernest Rutherford (actually his grad students) shot subatomic particles at gold atoms to try to probe the insides of those atoms. To his surprise, he found that instead of being one continuous glob, atoms actually had most of their mass concentrated in a small nucleus at the center of the atom. This quickly…

More Sailing

There’s an interesting question in the comments of the last solar sail post: I have a question that’s been bugging me about solar sails for ages: what about the fact that light pressure falls off over distance? Every time I see the idea discussed, this is never mentioned… He’s right. As the sail gets farther…

Falling Electrons

Not long ago I wrote about one of the conceptual problems between intro mechanics and intro E&M from the freshman physics standpoint: developing a sense of the size of units between the two subjects. For instance, accelerating a spacecraft to escape velocity is no easy feat, but accelerating an electron to escape velocity only requires…